I have been working on this for days. I built a server using the guide in Perfect Server Ubuntu 10.04, specifically using Postfix/Courier/SquirrelMail.

The SquirrelMail part of it sends and receives perfectly. I can receive using a MUA such as Outlook or Thunderbird, using both IMAP and POP3. However, I cannot get it to send at all. It simply times out.

Then entry in /var/log/mail.log that seems to match the connection attempt is:

I can connect from a remote host via "telnet domainName.com 25" and even send an email like that. Thinking about it, that's no different than the way SquirrelMail does it other than showing that port 25 is open.

Thinking that it was a problem with "smtpd_recipient_restrictions", I commented out the ISPConfig3 line and deleted the "check_recipient_access" that ISPConfig3 uses to whitelist, but it made no difference at all.

It seems like it may be an authorization problem, but I'm at a loss. Here is my main.cf:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific: Specifying a file name will cause the first
# line of that file to be used as the name. The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

I don't think it is a firewall issuse, FalKo, because I was able to telnet from a server in another part of the world to this server on port 25. I'm including the iptaples (maintained through ispconfig3). Maybe you'll see something I don't:

Are you absolutely sure then that your email client settings are ok? There should at least be something in the mail log when you try to connect...

Click to expand...

I'd like to thank you, Falko, for your attempts to help. After reading a lot and just sitting down and reasoning for a while, I've concluded that the data center where we rent the server has port 25 blocked to outgoing traffic.

Your guides on this website are absolutely great. I followed the guide for the Perfet Server using Ubuntu 10.04 LTS. Everything else worked, so my reasoning is that this should have worked as well.

This enables the smtp daemon to send through the submission port, 587. After updating my email client (Thunderbird) to reflect 587 instead of 25, and adding port 587 to ISPConfig's firewall rule, sending worked. Since the only thing I really changed was the outbound port (from 25 to 587), I must conclude that the data center provider has outbound port 25 traffic blocked.

One last question, Falko: if I remove 25 from the firewall rule, that should effetively block inbound traffic on port 25. Will internal, localhost, email still work even though I block the port from inbound requests?

One last question, Falko: if I remove 25 from the firewall rule, that should effetively block inbound traffic on port 25. Will internal, localhost, email still work even though I block the port from inbound requests?